Dilation catheters without ultrasound capability are well known and accepted. For example, angioplasty for coronary and leg arteries is common. Various companies market dilation catheters, including: SciMed Life Systems, Minneapolis, Minn.; Advanced Cardiovascular Systems, Santa Clara, Calif.; and USCI, Billerica, Mass.
Catheters for ultrasound imaging, especially for imaging coronary artery geometry, are also well known and are marketed by several companies including: Diasonics, Milpitas, Calif.; Cardiovascular Imaging Systems, Sunnyvale, Calif.; Endosonics, Pleasanton, Calif.
The benefits of a single catheter providing both dilation and ultrasound imaging, rather than two separate catheters, include decreased cost and catheterization time. Decreasing catheterization time allows a given catheterization facility and staff to serve more patients; among other benefits, this fact will likely decrease the patient's cost. Also, certain patients find catheterization somewhat frightening and uncomfortable. Presumably, they would prefer a faster procedure.
The potential for a combined dilation/imaging catheter has been recognized, for example, in U.S. Pat. No. 4,951,677--Crawley, et. al., describing a catheter sheath with a dilation balloon mounted over an ultrasound transducer so that an area can be imaged while it is opened with the balloon. This device, however, has certain limitations. It is not adapted for use with the steerable guidewires that physicians routinely use to guide catheters or other invasive devices into a desired arterial branch or other location. In addition, the disclosed catheter requires imaging through both the sheath and the balloon materials. As will be appreciated by those of skill in the art, this limits image quality because it is difficult to entirely rid a balloon of air bubbles. Since the bubbles are strong acoustic reflectors, they degrade image quality. Also, each layer of material between the ultrasound transducer and the artery creates opportunities for signal attenuation, which decreases sensitivity, and for acoustic reverberations, which introduce imaging artifacts. Finally, the disclosed catheter is of a larger diameter than is necessary for imaging with a given probe because the transducer is covered by both the sheath and the balloon, rather than just the sheath.
A catheter disclosed in U.S. Pat. No. 4,841,977--Griffith et al. shows a type of transducer array with a covering dilation balloon. The disclosed device is not, however, well suited to imaging when the balloon is deflated. In addition, the described system produces poor quality two-dimensional ultrasound images because of the limited number of different ultrasound data lines available to form each image.
U.S. Pat. No. 4,917,097--Proudian, et. al. describes a dilation/imaging catheter in which a large number of transducers, e.g., sixty-four, are arranged in an array and interfaced to special purpose integrated circuits mounted beside the transducer array at the distal end of the catheter. The balloon is slightly proximal of the array. The arrangement uses a steerable guidewire for catheter placement but exhibits a number of significant limitations. For example, the ultrasound transducers, circuits, and signal processing hardware incorporated into the catheter are substantially more complex than the corresponding elements of a mechanically scanned (rotating) system. In addition, the catheter slides along in contact with the artery (or other lumen) wall whenever the ultrasound imaging plane is moved, thereby failing to minimize trauma.
Thus, it can be seen that there is a long recognized, yet unfulfilled need for a catheter design which incorporates both a dilation balloon and an ultrasound imaging probe which, for reasons of simplicity and cost, is preferably mechanically rotated. Moreover, it would be desirable to provide such a catheter that is manipulated into place with a steerable guidewire for ease and speed of use. It would also be desirable to provide such a catheter design that minimizes cross-sectional area so as to be useable in small lesions, arteries or lumens. It is therefore an object of this invention to provide a catheter apparatus for combined balloon dilation and ultrasonic imaging. Another object of the present invention is to provide a dilation/imaging catheter of small cross-section in its distal length. A further object of the invention is to provide a single lumen/dual lumen transition in a catheter that facilitates passing the guidewire from the single lumen and into a specified lumen of the dual lumen section of catheter. Another object of the present invention is to provide methods of using catheters. An additional object of the present invention is to provide a method of backloading a guidewire from a single lumen section of a catheter and into a chosen lumen of a dual lumen section.